A vehicle device used, for instance, for a car navigation device needs to store (back up) a wide variety of data. Meanwhile, in a vehicle environment, the voltage value of a battery voltage supplied from a vehicle-mounted power source (vehicle-mounted battery) may occasionally decrease (the battery voltage may be occasionally interrupted) for a moment due, for instance, to cranking at engine startup or vibration-induced temporary connector disconnection. A remedial action taken in the past when the battery voltage was momentarily interrupted was, for example, to instantaneously switch a microcomputer from an awake state to a sleep state or connect a large-capacity capacitor. In recent years, however, it is difficult to take such a remedial action due to cost and size considerations because the power consumption of microcomputers has been increased. Incidentally, a technology for retaining stored data (preventing the loss of stored data) is disclosed in Patent Literature 1.